Don't know whether its true or not, love him or hate him, he's doing his time 'like a man' as they say. Gotta respect a guy for that.
Usually, federal prison isn't that tough. State prisons are the places that things like you see in HBO series Oz occurs.

Level 6 is no joke though. Usually reserved for high level, dangerous, fed offenders. Most fed offenders, even level 6 are usually no danger to each other. Drug Lords, mafia bosses, maybe the occassional serial rapist/murderer if they are not in state prison and have broken a federal law.